This paper discusses a set of observations, many of which are novel, concerning differences between the adjectival modals _certain_ and _possible_ and their adverbial counterparts _certainly_ and _possibly_. It argues that the observations can be derived from a standard interpretation of _certain_/_certainly_ as universal and _possible_/_possibly_ as existential quantifiers over possible worlds, in conjunction with the hypothesis that the adjectives quantify over knowledge and the adverbs quantify over belief. The claims on which the argument relies include the following: (i) knowledge (...) implies belief, (ii) agents have epistemic access to their belief, (iii) relevance is closed under speakers’ belief, and (iv) commitment is pragmatically inconsistent with explicit denial of belief. (shrink)